Process for treating paper



United States Patent Ofiice 3,044,895 PRCES FGR TREATING PAPER Larry Z.lsaacson, Cincinnati, Ohio, assignor to Formica Corporation, Cincinnati,()hio, a corporation of Delaware No Drawin Filed Dec. 9, 1957, Ser. No.701,319 2% Claims. (Cl. 117-=-6) This invention relates to a process fortreating paper Webs with phenolic resins and to the product preparedthereby. More particularly, this invention relates to a method forproducing phenolic resin impregnated paper particularly for use as coresheets in the manufacture of laminates. Still further, this inventionrelates to the method of treating paper with water until said paper iswetted and introducing said wetted paper into a homogeneous mixture of awater-soluble phenolic resin and a water-insoluble fusion phenolic resindispersed in an inert mutual solvent for the two resins and drying thepaper web.

One of the objects of the present invention is to produce paperimpregnated with phenolic resins to be used as the core sheets oflaminated articles. A further object of the present invention is toproduce phenolic resin impregnated paper having the required electricalproperties by use of an expedient and economic process. These and otherobjects of the present invention will be discussed in greater detailhereinbelow.

The use of phenolic resin impregnated paper as core sheets for laminateshas long been known in the art. Various methods for impregnation ofthese paper Webs with the electrical grade phenolic resin have beentried and although many of these processes have been successful in theproduction of a desirable product, the processes of the prior art havein many instances left a great deal to be desired, either because of themultiplicity of steps involved, the time factor and/or the economicfactor of cost of production. I have discovered that by preparing ahomogeneous dispersion of a water-soluble phenolformaldehyde resin and awater-insoluble fusible phenolform-aldehyde resin dispersed in a commoninert mutual solvent I can treat the paper in a satisfactory, expedientand economical process which avoids a number of the steps of the priorart and yet produces a completely satisfactory product. This isaccomplished by wetting the paper web prior to its introduction into themixed resin dispersion. This Wetting of the paper web can beaccomplished in a plurality of ways, for instance, the paper Web canbe'passed through a water bath or the paper Web can be sprayed on bothfaces with water or the paper web can be exposed to live steam or passedthrough a pair of wetted rollers or a plurality of the same. The mostpractical method, particularly from the standpoint of uniform wettingsis the spraying technique and this is preferred. The paper as normallyreceived will contain 5% of moisture although seemingly in a dry state.The addition of as small an amount as 1% of additional moisture willenhancevthe penetration of the water-soluble phenolic component into thefibers. Much larger additions of moisture are needed, however, in orderto develop maximum penetration. A total of about of added Water over andbeyond the original water content, i.e. a final water content of isnecessary in order to assure maximum penetration. Larger quantities ofwater may be added such as water up to about 40% over and beyond theoriginal moisture content, but it is to be noted that after a total of15% of Water has been added to the paper web, no significant furtherimprovement is achieved. As a consequence, for practical purposesassuming that the original paper web contains approximately 5% ofmoisture, there is added water in an amount to approximate 10% to 25% ofadded moisture.

In the preparation of the resin impregnating bath, one preparesseparately two different phenolic resins; a watersoiuble phenolic resinand a separately prepared waterinsoluble phenolic resin. Thislatterclass of resins is frequently identified as a spirit-solublephenolic resin or an electrical grade phenolic resin. In the preparationof the water-soluble phenolic resin, one may use phenol and formaldehydeas the starting ingredients in a mol ratio varying between about 1:1 and1:3, respectively, but preferably 121.2 to 1:25 phenol to formaldehyde,respectively. In order to achieve water solubility in this class ofresins, a number of factors must be kept in mind, for instance, thenumber of methylol groups should be kept high while the degree ofcondensation is kept low. The amount of free formaldehyde should be keptat a minimum in order to avoid loss in yield, odor and toxicity. Thesephenol-formaldehyde resins may be reacted on either the alkaline or theacid side of the pH range. Since difiiculty in control of the reactionon the acid side is sometimes experienced, it is preferred that thereaction be carried out on the alkaline side for better Water solubilitycharacteristics. To accomplish this, one may use an alkaline materialsuch as the alkali metal hydroxides and alkaline earth metal hydroxides,their oxides, carbonates and the like. Additionally, one may useammonium hydroxide or the organic primary amines such as methyl amine,ethyl amine, propyl amine and the like. For best results, sodiumhydroxide, triethyl amine and the like should be used. The temperatureat which the reaction is carried out is not critical and may be variedbetween about 40 C. and 100 C. but preferably between 60 and C. ,Whenlower temperatures are used such as 40 C., the reaction time islengthened prior to reaching a low fre e' formaldehyde content and forthis reason the middle temperatures are preferred. At 40 C. it may welltake as long as 16 hours'to achieve the desired free formaldehydecontent. At 60 to 80 C. the reaction time is between about 1 and 2hours. The use of higher temperatures such as 100 C. will ordinarily beavoided because of the risk of producing too much 18% by weight ofwater-soluble phenolic resin solids based on the total Weight of resinsolids. The waterinsoluble phenolic resin will be present in acorresponding amount, namelscbetween about to about 78% by weight ofinsoluble resin solids based on the total weight of resin solids.Preferably, the insoluble resin solids will be present in an amountvarying between 89% and 82% by weight of insoluble resin solids based onthe total weight of resin solids. v

The water-insoluble phenolic resin may be prepared by reactingformaldehyde with a phenol. Among the phenols which may be used in thepractice of the processof the present invention to prepare thewater-insoluble phenolforrnaldehyde resin are phenol per se, or one ofthe.

cresols, such as meta-cresol, para-cresol, and ortho-cresol, xylenol, ormixtures of these phenols coreacted with formaldehyde. The meta-cresolis preferred. Frequently, it is desirable to make use of a mixture ofphenols in making the water-insoluble phenolic resin such as a mixPatented July 17, 1962 ture of meta-cresol and xylenol-formaldehyderesins or cresol-aniline-formaldehyde resins and the like. Aconsiderable number of these resinous materials and their methodofpreparation are well known in the art. Among the xylenols which may beused in the resins of the present invention are 2,3-dimethyl phenol,3,4-dimethyl phenol, 3,5-dimethyl phenol, 2,6-dimethyl phenol, 2,4-dimethyl phenol, 2,5-dimethyl phenol and the like.

Among the mutual inert solvents for the two separately prepared phenolicresins used in the present invention are those organic materials havinga boiling point not greater than about 150 C. that are normally liquidsuch as the monohydric alcohols including methanol, ethanol, or theketones such as acetone, methylethyl ketone, diethyl ketone, ethylpropylketone, dipropyl ketone, and the like. It is sometimes desired to use amiscible blend of one of the above-recited solvents with an aromaticsolvent such as benzene, toluene, xylene, and the like. Ethanol aloneprovides a very desirable solvent mutually inert to each of the resinouscomponents. Equal portions of ethanol and toluene also make a desirablesolvent. Still further, equal portions of ethanol, toluene and methylethyl ketone make a desirable solvent mixture. For most purposes, apolar-type solvent or mixture thereof is to be chosen.

The paper treated in accordance with the process of the presentinvention may be a cellulosic type paper, of which many areconventionally known in the art, including kraft paper. After the paperto be treated has been wetted with the water and passed through theresin impregnating bath, the paper is passed through a drier heated at atemperature between about 110 and 160 C. in order to drive off thevolatiles only in the paper Web. The residence time in the drier will bedetermined by the temperature of the drier. Longer residence times willbe required at the lower temperatures and shorter residence at thehigher temperatures. After the paper has evolved from the drier, it isthen rolled and stored or it may be used at once.

The amount of total resin solids present in the impregnating bath may bevaried over a fairly substantial range such as between about solids toabout 80% solids. Preferably, for optimum results, the total percent ofresin solids should be between and 60% by weight based on the totalWeight of resin solids and the dispersing medium.

In order that the concept of the present invention may be morecompletely understood, the following examples representing methods forthe preparation of the resins used in the present invention are setforth in which all parts are parts by weight unless otherwise indicated.These examples are set forth primarily for the purpose of illustrationand any specific enumeration of detail contained therein should not beinterpreted as a limitation on the case except as is indicated in theappended claims.

RESIN A A water-soluble phenol-formaldehyde resin is prepared byintroducing into a suitable reaction vessel equipped with thermometerand stirrer 940 parts of phenol, 1010 parts of a 37% aqueous solution offormaldehyde and 10 parts of triethyl amine. The charge is heated toabout 80 C. and is held at about that temperature to a water toleranceof 1000%. Thereupon, there is added 100 parts of ethyl alcohol and theresin solution is cooled to room temperature. A water tolerance of 1000%means that 10 parts of the resin solution can be diluted with 100 partsof water without any indication of permanent precipitation of resin fromsolution.

RESIN B A water-insoluble fusible phenolic resin is prepared byintroducing into a suitable reaction vessel equipped with a thermometer,stirrer and reflux condenser 1010 parts of a 37% aqueous solution offormaldehyde, 1100 parts of cresylic acid (a mixture of ortho-, meta-,and para-cresols, preponderantly meta-cresol), 165 parts of tung oil and30 parts of a 28% aqueous solution of ammonia. The charge is heated tothe reflux temperature and held at that temperature for about 30minutes. The reflux condenser is removed and the system is dehydrated byremoving about 640 parts of water. Thereupon, there is added 460 partsof toluene, 300 parts of dioctyl phthalate and 920 parts of ethylalcohol.

Example 1 23 parts of the resin A solution and 145 parts of the resin Bsolution are blended together and introduced into an impregnating tank.A web of kraft paper is sprayed with water to a water content of about15% moisture total. Thereupon, the wetted web is introduced into themixed resin impregnating bath, removed therefrom and passed through adrying oven, heated to a temperature of about 125-135" C. and on removalfrom the oven, is passed continuously to a roller and wound to form aroll of the resin impregnated paper.

In the preparation of the water-insoluble phenolic resin, one may usethe selected phenol to formaldehyde in a mol ratio varying between about1:1 and 1:2 but preferably about 1:1.25. A preferred catalyst would beammonia. The condensation should be carried to a well advanced stage soas to provide water-insoluble characteristics but maintain fusibility.It is sometimes desired to modify the water-insoluble phenolic resinwith a glyceride oil such as the tung oil shown hereinabove, includinglinseed oil, soya oil, caster oil, and the like. These oils may beeither non-drying, semi-drying or drying oils and may be present in anamount varying between about 5% and 15% by weight based on the totalweight of resin solids.

It is sometimes desirable to make use of a plasticizer for thewater-insoluble phenolic resin of which a plurality are well known inthe art including dibutyl phthalate, diamyl phthalate, dihexylphthalate, diheptyl phthalate, dioctyl phthalate and the like. Of these,the dioctyl phthalate is preferred. The amount of plasticizer that maybe used can be varied between about 10% and 20% by weight based on thetotal weight of resin solids.

When additives or modifiers are used in the preparation or use of theresinous materials used in the present invention such as the glycerideoils and the plasticizers, these materials are considered to be a partof the total of the resin solids inasmuch as they do not volatilizeduring the drying step and become a part of the resin impregnated paperweb.

I claim:

1. A process for treating paper webs comprising wetting a cellulosicpaper web containing not more than about 5% of Water with water in anamount ranging from about 1% to 40% by weight, based on the weight ofsaid web, impregnating the wetted web with a mixture of from about 5% to22%, by weight, based on total resin solids, of a water-solublephenol-formaldehyde resin and correspondingly from about to 78% byweight, based on total resin solids, of a water-insolublephenolformaldehyde resin, dispersed in a mutual, inert solvent, anddrying the impregnated cellulosic paper web.

2. A process for treating paper webs comprising wetting a cellulosicpaper web, containing not more than about 5% of water with water in anamount ranging from about 10% to 25% by weight, based on the weight ofsaid web, impregnating the wetted web with a mixture of from about 11%to 18%, by weight, based on total resin solids, of a water-solublephenol-formaldehyde resin and corresponding from about 89% to 82% byweight, based on total resin solids, of a water-insolublephenolformaldehyde resin, dispersed in a mutual, inert solvent, anddrying the impregnated cellulosic paper web.

3. A process for treating paper webs comprising wetting a cellulosicpaper web containing not more than about 5% of water by spraying saidweb with water in an amount ranging from about 1% to 40% by weight,based on the weight of said web, impregnating the wetted web with amixture of from about 5% to 22%, by weight, based on total resin solids,of a Water-soluble phenolformaldehyde resin and correspondinglyfromabout 95% to 78% by weight, based on total resin solids, of awaterinsoluble phenol-formaldehyde resin, dispersed in a mutual, inertsolvent, and drying the impregnated cellulosic paper web.

4. A process for treating paper webs comprising wetting a cellulosicpaper web containing not more than about 5% of water by spraying saidWeb with water in an amount ranging from about to 25% by weight, basedon the weight of said web, impregnating the wetted web with a mixture offrom about 11% to 18%, by weight, based on total resin solids, awater-soluble phenol-formaldehyde resin and correspondingly from about89% to 82% by weight, based on total resin solids, of a Waterinsolublephenol-formaldehyde resin, dispersed in a mutual, inert solvent, anddrying the impregnated cellulosic paper web.

5. A process tortreating paper webs comprising wetting a cellulosicpaper web containing not more than about 5% of water with water in anamount ranging from about 1% to 40% by weight, based on the weight ofsaid web, impregnating the wetted Web with a mixture of from about 5% to22%, by weight, based on total resin solids, of a water-solublephenol-formaldehyde resin and correspondingly from about 95 to 78% byweight, based on total resin solids, of a Water-insolublecresol-formaldehyde resin, dispersed in a mutual, inert solvent, anddrying the impregnated cellulosic paper web.

6. A process for treating paper webs comprising wetting a cellulosicpaper web containing not more than about 5% of water with water in anamount ranging from about 1% to 40% by weight, based on the Weight ofsaid web, impregnating the wetted web with a mixture of from about 5% to22%, by weight, based on total resin solids, of a water-solublephenol-formaldehyde resin and correspondingly from about 95% to 78% byweight, based on total resin solids, of a water-insolublecresol-xylenolformaldehyde resin, dispersed in a mutual, inert solvent,and drying the impregnated cellulosic paper Web.

7. A process for treating paper webs comprising wetting a cellulosicpaper Web containing not more than about 5% of water with water in anamount ranging from about 1% to 40% by weight, based on the weight ofsaid web, impregnating the wetted web with a mixture or from about 5% to22%, by weight, based on total resin solids, of a water-solublephenol-formaldehyde resin and correspondingly from about 95% to 78% byweight, based on total resin solids, of a water-insolublecresol-aniline-formaldehyde resin, dispersed in a mutual, inert solvent,and drying the impregnated cellulosic paper web.

8. A process for treating paper webs comprising wetting a cellulosicpaper web containing not more than about 5% of water by spraying saidweb with water in an amount ranging from about 1% to 40% by weight,based on the weight of said Web, impregnating the wetted web with amixture of from about 5% to 22%, by weight, based on total resin solids,of a Water-soluble phenoltormaldehyde resin and correspondingly fromabout 95 to 78% by weight, based on total resin solids, of awaterinsoluble cresol-forrnaldehyde resin, dispersed in a mutual, inertsolvent, and drying the impregnated cellulosic paper web.

9. A process for treating paper webs comprising wetting a cellulosicpaper web containing not more than about 5% of water by spraying saidweb with Water in an amount ranging from about 1% to 40% by weight,based on the Weight of said web, impregnating the wetted web with amixture of from about 5% to 22%, by weight, based on total resin solids,of a water-soluble phenol-formaldehyde resin and correspondingly fromabout to 78% by weight, based on total resin solids, of a Waterinsolublecresol-xylenol-formaldehyde resin, dispersed in a mutual, inert solvent,and drying the impregnated cellulosic paper Web.

10. A process for treating paper Webs comprising wetting a cellulosicpaper web containing not more than about 5% of water by spraying saidweb with water in an amount ranging from about 1% to 40% by weight,based on the weight of said web, impregnating the wetted web with amixture of from about 5% to 22%, by weight, based on total resin solids,of a water-soluble phenolformaldehyde resin and correspondingly fromabout 95% to 78% by weight, based on total resin solids, of awaterinsoluble cresol-aniline-formaldehyde resin, dispersed in a mutual,inert solvent, and drying the impregnated cellulosic paper web.

11. A process for treating paper webs comprising Wetting a cellulosicpaper Web containing not more than about 5% of water by spraying saidweb with water in an amount ranging from about 10% to 25% by weight,based on the Weight of said Web, impregnating the wetted web with amixture of from about 11% to 18%, by weight, based on total resinsolids, of a water-soluble phenol-formaldehyde resin and correspondinglyfrom about 89% to 82% by weight, based on total resin solids, of awater-insoluble cresol-formaldehyde resin, dispersed in a mutual, inertsolvent, and drying the impregnated cellulosic paper web.

12. A process for treating paper webs comprising Wetting a cellulosicpaper Web containing not more than about 5% of water by spraying saidweb with water in an amount ranging from about 10% to 25 by Weight,based on the Weight of said web, impregnating the wetted web with amixture of from about 11% 'to 18%, by weight, based on total resinsolids, of a Water-soluble phenol-formaldehyde resin and correspondinglyfrom about 89% to 82% by weight, based on total resin solids, of awater-insoluble cresol-xylenol-formaldehyde resin, dispersed in amutual, inert solvent, and drying the impregnated cellulosic paper web.

13. A process for treating paper webs comprising wetting a cellulosicpaper web containing not more than about 5% of water by spraying saidweb with water in an amount ranging from about 10% to 25 by weight,based on the weight of said web, impregnating the wetted web with amixture of from about 11% to 18%, by weight, based on total resinsolids, of a water-soluble phenolformaldehyde resin and correspondinglyfrom about 89% to 82% by weight, based on total resin solids, of awaterinsoluble cresol-aniline-formaldehyde resin, dispersed in a mutual,inert solvent, and drying the impregnated cellulosic paper web.

14. A process for treating paper webs comprising wetting a cellulosicpaper web containing not more than about 5% of Water by spraying saidweb with Water in an amount ranging from about 10% to 25 by weight,based on the weight of said web, impregnating the wetted web with amixture of from about 11% to 18%, by weight, based on total resinsolids, of a water-soluble phenol-formaldehyde resin and correspondinglyfrom about 89% to 82% by weight, based on total resin solids, of aWater-insoluble cresol-formaldehyde resin, dispersed in ethanol, anddrying the impregnated cellulosic paper web.

15 A process for treating paper Webs comprising Wetting a cellulosicpaper Web containing not more than about 5% of water by spraying saidweb with water in an amount ranging from about 10% to 25% by weight,based on the weight of said web, impregnating the wetted Web with amixture of from about 11% to 18%, by weight, based on total resinsolids, of a water-soluble phenol-formaldehyde resin and correspondinglyfrom about 89% to 82% by Weight, based on total resin solids, of awater-insoluble cresol-xylenol-forrnaldehyde resin,

7 dispersed in ethanol, and drying the impregnated cellulosic paper web.

16. A process for treating paper webs comprising wetting a ccllulosicpaper web containing not more than about of water by spraying said webwith water in an amount ranging from about to by weight, based on theweight of said Web, impregnating the wetted web with a mixture of fromabout 11% to 18%, by weight, based on total resin solids, of awatersoluble phenol-formaldehyde resin and correspondingly from about89% to 82% by weight, based on total resin solids, of a water-insolublecresol-aniline-formaldehyde resin, dispersed in ethanol, and drying theimpregnated cellulosic paper web.

17. A process for treating paper webs comprising Wetting a cellulosicpaper web containing not more than about 5% of water by spraying saidweb with Water in an amount ranging from about 10% to 25% by weight,based on the weight of said web, impregnating the wetted web with amixture of from about 11% to 18%, by Weight, based on total resinsolids, of a Water-soluble phenol-formaldehyde resin and correspondinglyfrom about 89% to 82% by weight, based on total resin solids, of awaterinsolub1e cresol-formaldehyde resin, dispersed in a mixture ofethanol and toluene, and drying the impregnated cellulosic paper web.

18. A process for treating paper webs comprising wetting a cellulosicpaper web containing not more than about 5% of water by spraying saidweb with water in an amount ranging from about 10% to 25 by weight,

based on the weight of said web, impregnating the wetted web with amixture of from about 11% to 18%, by weight, based on total resinsolids, of a water-soluble phenol-formaldehyde resin and correspondinglyfrom about 89% to 82% by weight, based on total resin solids, of awater-insoluble cresol-xylenol-formaldehyde resin, dispersed in amixture of ethanol and toluene, and drying the impregnated cellulosicpaper Web.

19. A process for treating paper webs comprising wetting a cellulosicpaper Web containing not more than about 5% of water by spraying saidweb with water in 8 an amount ranging from about 10% to 25 by weight,based on the weight of said web, impregnating the wetted web with amixture of from about 11% to 18%, by weight, based on total resinsolids, of a water-soluble phenol-formaldehyde resin and correspondinglyfrom about 89% to 82% by weight, based on total resin solids, of awater-insoluble cresol aniline-formaldehyde resin, dispersed in amixture of ethanol and toluene, and drying the impregnated cellulosicpaper web.

20. A process for treating paper webs comprising wetting a cellulosicpaper web containing not more than about 5% of water by spraying saidweb with water in an amount ranging from about 10% to 25 by weight,based on the weight of said web, impregnating the wetted web with amixture of from about 11% to 18%, by weight, based on total resinsolids, of a water-soluble phenolformaldehyde resin and correspondinglyfrom about 89% to 82% by weight, based on total resin solids, of awater-insoluble cresol-formaldehyde resin, dispersed in a mixture ofethanol, toluene and methylethyl ketone, and drying the impregnatedcellulosic paper web.

References Cited in the file of this patent UNITED STATES PATENTS1,966,458 Novak July 17, 1934 2,343,095 Smith Feb. 29, 1944 2,554,128Spokes May 22, 1951 2,702,758 Uhlig ,Feb. 22, 1955 2,708,645 Norman May17, 1955 2,721,815 Mullen Oct. 25, 1955 2,732,295 Hollenberg Jan. 24,1956 2,739,908 Marsh Mar. 27, 1956 2,758,101 Shappell Aug. 7, 19562,801,198 Morris et a1 July 30, 1957 2,825,706 Sanders Mar. 4, 1958OTHER REFERENCES Bauer: Method for Combining Phenolic Resins and Paper,TAPPI Section, pages 28-30, Paper Trade Journal, vol. 125, N0. 3, pages-52.

1. A PROCESS OF TREATING PAPER WEBS COMPRISING WETTING A CELLULOSICPAPER WEB CONTAINING NOT MORE THAN ABOUT 5% OF WATER WITH WATER IN ANAMOUNT RANGING FROM ABOUT 1% TO 40% BY WEIGHT, BASED ON THE WEIGHT OFSAID WEB, IMPREGNATING THE WETTED WEB WITH A MIXTURE OF FROM ABOUT 5% TO22%, BY WEIGHT, BASED ON TOTAL RESIN SOLIDS, OF A WATER-SOLUBLEPHENOL-FORMALDEHYDE RESIN AND CORRESPONDINGLY FROM ABOUT 95% TO 78% BYWEIGHT, BASED ON TOTAL RESIN SOLIDS, OF A WATER-INSOLUBLEPHENOLFORMALDEHYDE RESIN, DISPERSED IN NUTUAL, INERT SOLVENT, AND DRYINGTHE IMPREGNATED CELLULOSIC PAPER WEB.